1. Field of the Invention
The invention relates to a seatback frame structure.
2. Description of Related Art
Recently, some seatback frames are being made with resin material (see Japanese Patent Application Publication No. 2007-161237 (JP 2007-161237 A), for example). With a seatback frame made with such resin material as well, when a reclining mechanism is provided on the seatback frame, the seatback frame is fixed by a fastening member such as a bolt to a bracket (a joining member) that is joined to the reclining mechanism.
When a vehicle is involved in a rear collision, a seated occupant moves toward a seat rear side due to inertia force, such that a load toward the seat rear side is input to the seatback frame from the seated occupant. If the load input to the seatback frame is greater than the fastening force by the fastening member between the bracket (i.e., the joining member) and the seatback frame, the seatback frame will move relative to the fastening member. As a result, an inner peripheral portion of a hole in the seatback frame through which the fastening member is inserted may abut against the fastening member, and the load input to the seatback frame may end up concentrating at the inner peripheral portion of this hole, for example. Therefore, it is desirable to reduce the concentration of the load at the fastening portion of the seatback frame.